In order to prevent delicate state-of-the-art electronic equipment onboard naval vessels from failure caused by adverse shock and vibration, shock and vibration isolation techniques have to be applied.
Specifically, modern electronically scanned radar systems (AESA) have very high requirements regarding platform stability in order to operate accurately. A relative movement between radar system and platform must be generally avoided and only a very small rotation deviation is tolerable.
A shock-isolation platform suitable for radar systems installed on vessels must therefore offer almost rigid behavior when subjected to accelerations up to 5 g but should act as a shock absorber when the load exceeds 5 g.
Typical and well-known damping means for such platforms are helical springs or wire rope isolators. However, this method does not ensure enough stability during normal naval vessel operation, resulting in rotatory motion of the system.
U.S. Patent Application Publication No. 2003/0075407A1 discloses a so-called Stewart platform for shock isolation of sensitive equipment on a vessel. The proposed shock-isolation platform is based on helical springs that do not have the needed damping properties outlined above for the protection of a radar system used on a vessel. The disclosed Stewart platform is not sufficiently stiff to ensure stability for the radar system to operate. Using this type of isolation structure requires a fixed predefinition of the spring rate. If a stiff spring is chosen, the platform will be stable when loaded up to 5 g, but in case of underwater detonation the acceleration will be transmitted and will damage electronic equipment. On the other hand, if one chooses soft springs, the platform will withstand an underwater detonation, but the radar will not be able to operate during ship motion because of insufficient stability and stiffness of the isolation structure.
Electrorheological or magnetorheological fluid (hereinafter designated as ERF and MRF, respectively) damping elements for a shock-isolation structure on a vessel are discussed in U.S. Pat. No. 6,752,250 B2. However, the very simple mounting principle does not meet the constructive requirements of a naval radar. The disclosed system acts mainly in one axis, making it impossible to fix a complex radar system to it.
As can be easily seen, the disclosed isolating structure can be exposed only to vertical shock. Due to the joints employed in the system, the system does not have any stiffness in horizontal direction, making it unsuitable for use on naval vessels. A further disadvantage of the disclosed structure is the complex control of its damping properties. Usually MRF or ERF damping elements have soft damping properties and the stiffness is increased only when needed. According to the requirements associated with a naval radar system, however, exactly the opposite is needed, i.e., the damping elements are permanently under high voltage to ensure very high stiffness. The stiffness is decreased only when a specific event occurs (shock, detonation etc.). The mentioned disadvantages render the structure disclosed in U.S. Pat. No. 6,752,250 B2 unsuitable for the protection of a naval radar contemplated by this invention.